1. Field of the Invention
The present invention relates to a light-emission material for an organic light-emitting diode.
2. Description of the Related Art
An organic light-emitting diode (OLED) (also referred to as organic electroluminescent device) is an LED with an organic layer serving as an active layer. OLEDs have been increasingly applied in flat panel displays due to advantages over other LEDs such as low voltage operation, high brightness, light weight, slim profile, wide viewing angle, and highly effective contrast ratio. The OLED is self-emitting and highly luminous, with wide viewing angles, fast response speeds, and a simple fabrication method.
Generally, OLEDs are composed of a light-emission layer sandwiched between a pair of electrodes. When an electric field is applied to the electrodes, the cathode injects electrons into the light-emission layer and the anode injects holes into the light-emission layer. When the electrons recombine with the holes in the light-emission layer, excitons are formed. Recombination of the electron and hole results in light emission. To achieve maximum efficiency of the operation of OLEDs, equilibrium between injecting and transmitting of electrons and holes must be achieved. Thus, it is an important objective for OLEDs to increase combination efficiency of electrons and holes in the light-emission layer. Accordingly, a host-guest system has been disclosed, wherein a light-emission layer doped with a small quantity of a highly efficient light-emission dopant (guest), has been used for increasing combination efficiency of carriers, for required color and sufficient brightness of the fabricated OLEDs. Note that the host delivery carrier does not need to be changed, for the color of the emitting light of the OLED to be the three colors: red, green, and blue, only the light-emission dopant needs to be changed.
Examples of host-quest systems include U.S. Pat. No. 645,645, wherein a phosphorescent OLED having a light-emission layer including a host material of phenanthroline (BCP) and a guest material of fac-tris(2-phenylpyridine)iridium (Ir(ppy)3) used as dopant doped in the host material is disclosed. U.S. Pat. No. 6,097,147 discloses a phosphorescent OLED, wherein, in the light-emission layer, the host material is carbazole biphenyl (CBP) and the guest material is 2,3,7,8,12,13,17,18-o ctaethyl-21H,23H-porphine platinum (II) (PtOEP).
Adachi, in the periodical “Appl. Phys. Lett.” (Vol. 78, No. 11, 12 Mar. 2001, pp. 1622-1624) discloses a phosphorescent OLED having a hole-blocker layer, wherein, in the light-emission layer, the host material is CBP and the guest material is iridium bis[2-(2′-benzo[4,5-a]thienyl)pyridinate-N,C. sup.3′]acetylacetonate (Btp2Ir(acac)).
Kwong, in the periodical “Appl. Phys. Lett.” (Vol. 81, No. 1, 1 Jul. 2002, pp.162-164) discloses a phosphorescent organic light-emitting device having a hole-blocker layer, wherein, in the light-emission layer, the host material is CBP and the guest material is Ir(ppy)3.
In 1999, Forrest discloses in Appl. Phys. Lett. 74, 442 (1999), an organic phosphorescent material, “PtOEP”, doped in CBP by evaporation. In 2001, Forrest further discloses in Appl. Phys. Lett. 78, 1622 (2001), a red phosphorescent material containing iridium, “Btp2Ir(acac)”, doped in CBP.